Technical Field
The present disclosure relates to a motor speed control system and a motor speed control method. More particularly, the motor speed control system and the motor speed control method of the present disclosure are capable of reducing magnetic force of a rotor and increasing motor operation efficiency.
Description of Related Art
In many industrials, operations of machines require a rotational movement. A motor is commonly used to produce this kind of rotational movement. The motor has become an indispensable device owing to its capability on converting magnetic energy or electrical energy into mechanical energy. There are various types of motors that can be applicable to different environments and operation conditions, such as induction motors and permanent magnet motors.
The conventional permanent magnet motor includes a stator, a rotor and a shell. The stator is composed of an armature coil and an armature core. The armature core is formed by stacking a plurality of silicon steel sheet, and the armature is located on the stator. The rotor is made of permanent magnetic material. The shell not only can fix the stator, but also can be used as a part of the magnetic circuit. Furthermore, inner-rotor permanent magnet motors can be classified into different types according to the types that the stator winds, such as two-phase, three-phase or five-phase permanent magnet motor, and the three-phase permanent magnet motor is the most popular. In general, the permanent magnet motor has high operation efficiency. In the permanent magnet motor, a torque is generated from interaction between the permanent magnet of the rotor and the stator coils to keep the synchronous speed. Recently, due to the constantly improved material of the permanent magnet and magnetic energy product, the permanent magnet motor can achieve very high operation efficiency.
However, the permanent magnet motor has the characteristics of slow starting time, and has insufficient torque at low speed, therefore its rotational speed takes a long time to reach a predetermined value. Furthermore, a complicated control system is required in the permanent magnet motor, thus the manufacturing cost of the motor is increased. Moreover, when the permanent magnet motor reaches the highest rotor speed, the power consumption of the motor is too large. Therefore, a motor speed control system and method having low cost, simple control, high-energy efficiency and high torque with maximum rotor speed is commercially desirable.